This issue was detected during accessibility audit on learner-facing pages in Workplace performed in August-September 2023 by AbleDocs.

Fieldsets are present in the filters dropdown without corresponding legends. Note that the legend must be the first element of the fieldset. Using a FIELDSET without the LEGEND is a failure under H71.

In the reportbuilder filters form we use "group" element to group together controls so we can display them in one line. The group element uses fieldset for it - https://github.com/moodle/moodle/blob/v4.3.0/lib/form/templates/element-group.mustache#L10-L20 . Since we do not add a legend, it fails accessibility audit.

It looks like this is a generic problem in Moodle. Another place where AbleDocs raised the same issue is the button group: